1. Field of the Invention
The present invention relates to a mobile communications network system, a mobile terminal, and a paging method for issuing a paging notification to, that is, paging, a mobile terminal through any radio system when a multimode mobile terminal receives a call under a communications environment in which radio waves of plural types of radio systems having different communication systems including a cellular system such as a PDC (personal digital cellular), an IMT (international mobile telecommunications)-2000, etc., a wireless LAN system such as an IEEE (institute of electrical and electronics of engineers) 802.11a/b, a Bluetooth system, etc. are used.
2. Description of the Related Art
Recently, in a mobile communications network system, there are plural types of radio systems having different communication systems. Furthermore, for example, in the cellular system, the fourth generation system has been studied and developed with a further higher-speed and larger-capacity system aimed at. In the wireless LAN system, the IEEE 802.11g, etc. has been standardized, and a new radio system such as a UWB (Ultra Wideband), etc. has been studied and developed. In the consideration of the above-mentioned status, it is considered that the radio systems would diversify increasingly in the future.
FIG. 10 shows one feature of the mobile communications network system of the Beyond IMT-2000 in which the service areas of various types of radio systems overlap each other.
That is, FIG. 10 shows the mobile communications network system including cellular systems 11 and 12 of 3G (third generation) and 4G (fourth generation), a wireless LAN 13, a Bluetooth system 14, and other radio systems 15 and 16. Under the environment of such wireless communications, there can be the communications performed by a multimode mobile terminal (hereinafter referred to as a mobile terminal) 18 capable of establishing communications using various radio systems 11 to 16.
In the above-mentioned background, a multimode mobile terminal capable of communicating with plural types of radio systems is actually being developed. First, there is a PHS (personal handyphone system)/PDC dual terminal, and in the future, it is expected to successfully develop a PDC/IMT-2000 dual terminal, an IMT-2000/IEEE 802.11b dual terminal, etc., and the study of a software radio technique is also actively proceeding.
The study of the control of a location under a communications environment in which radio waves of plural types of radio systems are used has been performed.
For example, in the following Non-patent Document 1, the contents relating to the location management database are emphasized, and the location management performed by the mobile terminal on plural types of radio systems is described.
Non-patent Document 2 describes the location registration and the paging performed by a control radio system commonly used in plural types of radio systems referred to as BANs (basic access networks).
Non-patent Document 3 describes the integration of a plurality of PCSs (personal communication systems). Two cases are assumed, that is, when only one radio system is location-registered, and a plurality of (two in this example) radio systems are location-registered. The method for paging a mobile terminal can be first calling through a radio system having the highest priority predetermined in advance, and then completing the calling procedure if a response is returned from the mobile terminal. If there is no response, the calling operation is continuously performed sequentially through the radio system having the highest priority until a response is returned from the mobile terminal.
Patent Document 1 describes a location registering method of a multimode mobile terminal for registering a location by detecting the degeneration of the radio wave status of one radio system and selecting another radio system having a better radio wave status. When plural types of radio systems can be used, a radio system is selected based on the priorities uniformly assigned to all terminals in advance.
Non-patent Document 4 describes a method for switching a radio system referred to as a vertical handoff used by selecting the optimum radio system during the communications of a mobile terminal.
In addition, Patent Document 2 describes a mobile terminal selecting the optimum radio channel from among a plurality of radio channels formed between a radio base station and a mobile terminal in each of a plurality of wireless communications systems based on a predetermined selection standard. The selection standard can be any one of the status of a mobile terminal, the (physical) status of a user of a mobile terminal, the communications contents between a mobile terminal and a destination terminal, the status of a destination terminal, the status of a radio channel, and the cost or the power consumption required for the communications between the mobile terminal and the destination terminal.
(Patent Document 1)
Japanese Patent Laid-Open No. 6-260990 (Abstract, Scope of Claim for the Patent)
(Patent Document 2)
Japanese Patent Laid-Open No. 2002-112347 (Abstract, Scope of Claim for the Patent, Embodiments of the Invention on page 10)
(Non-patent Document 1)
“Location Management in a Heterogeneous Network Environment”
Author: Qing Tian, Donald C. Cox (Stanford Univ.)
Published in: IEEE Wireless Communications and Networking Conference (WCNC) 2000
(Non-patent Document 2)
“MIRAI Architecture for Heterogeneous Network”
Author: Gang Wu, Mitsuhiko Mizuno (Communication Research Laboratory) and Paul J. M. Havinga (University of Twente, the Netherlands) Published in: IEEE Communication Magazine, February 2002
(Non-patent Document 3)
“Heterogeneous Personal Communications Services: Integration of PCS Systems”
Author: Yi-Bing Lin (National Chaio Tung Univ.), Imrich Chlamtac (Boston Univ.)
Published in: IEEE Communication Magazine, September 1996
(Non-patent Document 4)
“Vertical Handoffs in Wireless Overlay Networks”
Author: Mark Stemm, Randy H. Katz (U. C. Berkeley)
Published in: ACM Mobile Networking (MONET), 1998
There are the following problems with the above-mentioned conventional mobile communications network systems.
In Non-patent Document 1, the contents relating to the location management database are emphasized, and it is assumed that the mobile terminal performs location management on plural types of radio systems. However, there are no detailed descriptions as to how a radio system is selected and the paging is performed.
Since the Non-patent Document 2 describes the location registration and the paging performed by a control radio system commonly used in a plurality of radio systems referred to as BANs (basic access networks), the radio system for performing the location registration and the paging is fixedly determined. Therefore, it is assumed that traffic can concentrate on one radio system. Additionally, as a radio system for use during communications, there can be the method of selecting the optimum radio system different from a radio system for performing the paging. In this case, the interface of the radio system for use in the communications after the paging is activated, and a number of processes are required for reserving communications channels, etc. Therefore, there can be the problem of a delay of the communication starting time.
As in Non-patent Document 4, there can be the method of the mobile terminal selecting and using the optimum radio system during the communications. However, in this method, since the mobile terminal can select a radio system only during the communications of the mobile terminal, the optimum radio system cannot be necessarily selected when the communications of the mobile terminal are started.
In Non-patent Document 3, the location registration is performed on plural types of radio systems, that is, the location registration areas of plural types of radio systems can be managed as the location information about the mobile terminal currently not performing communications.
However, in Non-patent Document 3, a mobile terminal is called through a terminal having the highest-priority, and when a response is returned from the mobile terminal, the calling procedure is completed. Therefore, if the radio system having the highest priority is continuously applied, traffic concentrates on the radio system.
Patent Document 1 selects and location-registers the radio system having a good radio wave status when the current radio wave status degrades, and when the entire radio system is available, a radio system is selected and location-registered based on the priority set in advance. Therefore, a radio system for use in the paging cannot be selected.
According to Patent Document 2, the radio system is selected (switched) during the communications. Therefore, when the communications are started, the optimum radio system is not always selected. Furthermore, since only the mobile terminal selects a radio system, a radio system cannot be selected with the network status appropriately taken into account.
In addition, each type of the existing radio systems has a different feature respectively, and has its own merits and demerits. For example, the cellular system excels in the QoS (Quality of Service) guarantee technique for guaranteeing a predetermined communication speed by reserving a band for specific communications, and an area cover. However, it is hard to provide a high-speed transmission, and requires a relatively high-priced communications fee.
The wireless LAN can provide a high-speed transmission at a relatively low-priced communications fee. However, it provides a local area cover, and has not established a sufficient QoS guarantee technique at the present time.
Furthermore, in the current mobile communications network system, selecting the optimum radio system for a mobile terminal during paging has not been realized.